A gravure printing or roll coating method has conventionally been used so as to form a pattern on a siding material for outer wall (see Japanese Unexamined Patent Application, First Publication No. 2001-121078 and Japanese Unexamined Patent Application, First Publication No. 2003-001749). However, since an expensive printing plate is used in a gravure printing method, a pattern cannot be easily replaced and it was difficult to change or modify the pattern. Also, according to the gravure printing or roll coating method, a pattern can be printed only on a flat surface and it was difficult to achieve a pattern having three-dimensional impression.
Therefore, it was proposed to print using an ink jet system (see Japanese Unexamined Patent Application, First Publication No. Hei 10-278497). In the case of printing using the ink jet system, a drawing pattern can be freely and easily changed on demand and also printing can be carried out even if the printing surface has irregularity, and thus a drawing pattern having three dimensional impression can be provided.
However, characteristics required to the ink jet ink used in the siding for outer wall includes, in addition to characteristics required in a conventional ink jet ink, high weatherability which prevents fading even when exposed to sunlight, and physical strength such as adhesion with a substrate as a base, an undercoating layer, or a clear layer to be overcoated so as to protect the printed portion.
As a jet printing ink capable of forming an image on a non-absorbable material to be recorded such as siding material, for example, an ink prepared by dissolving or dispersing a coloring agent in a mixed solution of a resin and a solvent has conventionally being used.
The coloring agent includes dye-based and pigment-based coloring agents and a dye-based coloring agent is commonly excellent in dispersibility and color developability, but is likely to cause fading. Therefore, in colorfastness and weatherability, the pigment-based coloring agent is considered to be advantageous. Therefore, a pigment-based coloring agent (pigment), which is insufficient in stable dispersion but is excellent in light resistance, is generally used for outer wall siding.
As the film forming resin component of the ink composition for jet printer, various resins such as polyester resin, vinyl chloride-vinyl acetate copolymer resin, ethylene vinyl acetate copolymer resin, polyurethane resin, acrylic resin, styrene-acrylic resin, polyvinyl butyral resin, rosin-modified maleic acid resin, nitrocellulose and phenol resin are used alone or in combination.
However, in the case of a conventional ink composition for jet printer using these pigments and resins, when a wall material having a drawing pattern formed thereon using them is used as an outer wall material, the drawing pattern was inferior in weatherability and durability. Therefore, a conventional ink composition was not suited for use in the outer wall.
As described above, there has never been put an ink composition for jet printer, in which a pigment in an ink is sufficiently in the form of fine particles and stably dispersed to the degree which enables ink jet recording and also, when a pattern for outer wall is formed using this ink, the pattern has excellent weatherability and durability, into practical use.